火星陨石NWA 13763矿物岩石学特征及其岩浆演化

Mineralogical and ptrological characteristics of Martian meteorite NWA 13763 and magma evolution

NWA 13763陨石为一块新发现的辉长质辉玻无球粒火星陨石,辉长结构和次辉绿结构,主要矿物组成为辉石(45.1%,其中普通辉石36.1%,易变辉石9.0%)和斜长石(42.3%,几乎全部熔长石化),次要矿物组成为富硅相(5.1%)、橄榄石(2.7%)、磷酸盐矿物(2.4%)、钛铁矿(2.2%),含极少量钛磁铁矿和斜锆石。陨石中广泛发育“铁橄榄石+富硅相”二相后成合晶和“钙铁辉石+铁橄榄石+富硅相”三相后成合晶。辉石主晶核部贫铁富镁(Fs_(24.7-55.3)),边部富铁贫镁(Fs_(61.5-86.1));熔长石成分均一(An_(44.4-54.6Ab43.7-53.7));铁橄榄石(Fa_(84.5-97.7))全部以细粒状分布于后成合晶中。由钛铁氧化物固溶体计算得到岩浆结晶的氧逸度(FMQ)f_(O_(2))=-0.045,钛铁矿结晶温度约975℃。利用全岩成分和MELTS程序模拟计算表明,NWA 13763陨石的母岩浆液相线温度范围可能为1190~830℃,矿物结晶顺序由早到晚可能为:培长石→拉长石→橄榄石→单斜辉石→中长石→磷酸盐矿物→钛铁矿→富硅残余相。

NWA 13763 meteorite is a newly recovered Martian meteorite and classified as a gabbroic sherggottite with gabbro to sub-ophitic textures.The main mineral assemblages are pyroxene(45.1%,including augite 36.1%and pigeonite 9.0%)and plagioclase(42.3%,almostly change into maskelynite),while the secondary minerals are silica-rich phase(5.1%),olivine(2.7%),phosphate(2.4%)and ilmenite(2.2%),and very small amounts of titanomagnetite and baddeleyite.The symplektite of“Fe-rich olivine+silicon rich phase”and“Fe-rich olivine+hedenbergite+silicon rich phase”assemblages are extensive development in this meteorite.The core of main pyroxene is Fe-rich and Mg-poor(Fs_(24.7-55.3)),and its rim is Fe-poor and Mg-rich(Fs_(61.5-86.1)).The composition of maskelynite is uniform(An_(44.4-54.6Ab43.7-53.7)).Fe-rich olivines(Fa_(84.5-97.7))are distributed in the symplektite as a fine granular.The oxygen fugacity(FMQ)f_(O_(2))of NWA 13763 is-0.045,and the crystallization temperature of ilmenite is about 975℃.When using the MELTS program simulation it shows that the liquidus-solid temperature of the parent magma of NWA 13763 meteorite is from 1190℃to 830℃.The sequence of mineral crystallization from early to late may be bytownite→labradorite→olivine+clinopyroxene→andesine→phosphate mineral→ilmenite→silica-rich residual phase.